Attention has been directed to profile loss as a factor in improving the performance of turbine blades of the aforementioned type. The main cause of the profile loss is a loss caused by velocity distribution defects attributable to wake flows behind the blade trailing edges of the turbine blades. Thus, in order to reduce the profile loss, it is important to keep the velocity distribution defects as low as possible.
It has been known that a turbine blade whose blade trailing edge has a smaller thickness shows less velocity distribution defects. Many of turbine blades employ a blade trailing edge having a profile such that the blade suction side line and the blade pressure side line are connected by an arc corresponding to nearly the half of a true circle or by a straight line perpendicular to the camber line.
Where the turbine blade has such a profile that the blade trailing edge has a semicircular shape, the thickness of the blade trailing edge cannot be made smaller than the diameter of the semicircle. As a result, the blade trailing edge of the turbine blade becomes relatively large in thickness and produces significant wake flows, causing relatively large velocity distribution defects.
As conventional turbine blades configured to reduce the velocity distribution defects, the turbine blade disclosed in Patent Document 1 has been known, by way of example.
The trailing edge portion of the turbine blade disclosed in Patent Document 1 has such a curved surface that the radius of curvature gradually decreases from one of the blade suction side and pressure side lines toward the rear end located at the most downstream side as viewed in the fluid flowing direction, is the smallest at the rear end, and then gradually increases from the rear end toward the other of the blade suction side and pressure side lines up to the other of the blade suction side and pressure side lines.